Solutions of a formaldehyde substituted hydantoin, such as 1,3-dimethylol-5,5-dimethyl hydantoin (DMDM hydantoin), prepared in an anhydrous liquid solvent such as a polyhydroxy alcohol and/or an alkylene carbonate have previously been disclosed (see Schoenberg U.S. Pat. No. 5,037,843 issued Aug. 6, 1991). Such solutions particularly those employing propylene glycol as the solvent, now enjoy commercial success and display antimicrobial activity when used as preservative systems in personal care, cosmetic, and household products at use concentrations of typically less than about 1 weight percent of the product. Although in the Schoenberg solutions the solvents themselves are readily water miscible, they display no antimicrobial activity at the use concentrations employed.
For certain formulations, however, formulators now desire to incorporate as a preservative an aromatic alcohol particularly because such an alcohol can both demonstrate antimicrobial activity and be in liquid form. Such aromatic alcohols have a limited solubility in water.
It has now been discovered that formaldehyde substituted hydantoin is compatible with and soluble in such an antimicrobial liquid aromatic alcohol. Thus it would appear that a desirable antimicrobial solution for use as a preservative in the cosmetic field could be prepared by simply physically dissolving a formaldehyde substituted hydantoin in such an aromatic alcohol. However, such physical blends are not available as articles of commerce and hence must be prepared by the user from separate components in multistep procedures. Thus, there is a need and desire in the trade for liquid solutions of a formaldehyde substituted hydantoin in such an aromatic alcohol.
It is not practical to reprocess a Schoenberg solution to remove therefrom the Schoenberg solvent medium and to replace same with such a liquid aromatic alcohol. Also, addition of such an aromatic alcohol to a previously prepared Schoenberg solution is not practical because such addition reduces the concentration of resulting antimicrobial agents in the solution as diluted.
In order to supply to the using trade a solution of a formaldehyde substituted hydantoin in an aromatic alcohol, it is necessary to prepare an antimicrobial preservative solution which is not only an effective liquid preservative that is compatible with formulations with which it is to be used, but is also shelf stable at ambient conditions and economical to use. However, merely substituting a liquid aromatic alcohol for a polyhydroxy alcohol and/or alkylene carbonate in a solution preparation process such as described by Schoenberg in the '843 patent does not result in a practical preparation process because the solubility characteristics of the aromatic alcohols present different compatibility, stability and liquidity problems. A new and commercially practical process for directly preparing and synthesizing antimicrobial solutions of formaldehyde substituted hydantoin in an aromatic alcohol would be desirable.
The present invention provides both such a new and commercially practical direct synthetic process and new resulting product solutions which have unexpected value as antimicrobial liquid preservatives.